This is a question that can only really be answered by yourself. Anything that we say is just going to be what we like ourselves. Personally, I have British Paras as well as British infantry. Where does your interest lie and what do you like the most, be that vehicles or whatever. Of course, there are a number of US vehicles that can be used by both sides or you can go for true British ones if you go with a British force.
"Right! Open this door or I'll take away every piece of Warhammer you've ever owned!"
Thanks for all the suggestions. I have looked into some battles around the time and I'm going to recreate the Battle of Carentan (Bloody Goulch). Therefore I am going for the US 101st Airborne. Thanks again for the help!